I thinking about creating a wildcat cartridge. It requires reducing the the rim diameter on a brass casing by 0.008. I'd welcome any suggestions on the best way to do this. I've got 50 casing that I need to do this on. Is the best plan to find a small CNC shop to do the work or send the casings to a gunsmith and have them do the work? I don't see myself chucking these in a drill then hitting them with sandpaper or a file. I'd rather have a more professional result.

Im setting here thinking of what I have at my reloading bench that would trim the case rim. You might be able to rig up some way to use a hand held neck turner but instead of it riding in the case mouth it could ride through through the primer flash hole. It would be easier to have a machine shop chuck them in a lathe though.

Reducing a rim dia is not going to make the case weak.It is no problem,
However,if at all possible,you might consider opening up the chamber rim recess and adjusting the extractor.(Or the boltface,depending..)You only have to do that once.
I have access to a fine old South Bend with a 5C collet setup and a taper attachment.While I could get a soft collet and bore it,likely I would just make a shouldered bushing to fit in a 5c collet,with the ID tapered to fit the body of the cartridge.Then I might slice one side with a bandsaw so it could clamp a bit.
If you have to do it stone knives and bearskins,tell me what you have to work with,and I'll try to give you a setup idea.
If you have a good quality drillpress with a fairly precise,rigid spindle we can make that work.Its a spindle.What is your parent case?

Years ago, when I first made my 416 Rigby you couldn't buy cases. You could only get loaded rounds from Rigby.

BUT:

You could trim the belts off 460 Weatherby brass, run it through a 416 sizer die and you were good to go.

What I did was make a mandrel to fit the inside of the case. I had a point on the mandrel to fit in the primer flash hole (I had deprimed the brass. Then use a live center on the outside of the primer pocket. This allowed the case to run true without any wobble. Then set the lathe speed pretty fast and took light cuts.

This made some pretty accurate brass. Don't have to do it any more because you can get the 416 brass now. Plus since it kicks like a mule I don't shoot it enough to really wear out the brass.

I assume you already have a chamber reamer for your wildcat I would just get a 5C machinable collet and ream it to insert the case and turn the rim down on a lathe. Each one would take only seconds and you don’t have to pay for any CNC programming.

Mr. Morris is correct. I convert .303 to make brass shotshell cases for my .44 mag Smith. Have to reduce the rim a little and thin the case head to match pistol primer depths but it's easy to do on a lathe with the cases firmly held in a proper size 3C collet. (Guess I'm making "wildcat" shotgun ammo?)

I initially thought running the chamber reamer into a soft collet was a natural.Then I thought about the possibility of the slits in the collet catching a flute on a straightfluted reamer. True,it might not catch as the number of flutes vs slits are different,but might not isn't very good if you know that guy Murphy.
For only 50 cases,even a delrin shouldered bushing to go in maybe a 3/4 in collet is a quick,easy bet

Let's just assume there isn't any neck or shoulder to deal with. For arguments sake lets just call this a straight walled pistol casing. I have a drill press available but no lathe. Is this as simple as just finding the appropriate 3c/5c collet that I can chuck in my drill press then using a file just hold it on the casing rim as it spins?

I'm guessing you would do this a little at a time, stop, measure, then do it again until you remove the appropriate amount of material? If I making this harder than I should or am trying to make it simpler than it is please chime in. This is a first for me. I don't have machining experience. Even a 3c collet would be a new one on me.

p.s. Let me clarify...I'm thinking about a collet that would fit inside the casing to hold it...not outside.

Jmorris,I understand that.30 years of prototyping,modelmaking,moldmaking.I have machined plenty of soft collets and soft jaws. great tools.
Suppose you have a 4 flute reamer in a 3 slit collet.3 flutes are under cutter pressure while 1 flute is jumping the gap in the slit in the collet. that cutting edge is jumping an interrupted cut while the cutter pressure fom the other 3 flutes wants to deflect it into the cut. murphy's law tells me when the full length of that straight flute cutting edge jumps the collet slot the reamer will spring over a bit(remember,the reamer pilot is not running on a rifle bore) and a dig in MAY happen on that flute.
snap!There is also likely going to be a hole roundness issue,like getting a 3 sided hole with a 2 flute drill.
i
If it were a spiral flute reamer,probably no problem.I'll agree it might work,but you are on very thin ice.
I'm used to fairly expensive,high stakes parts where taking chances is ill advised.
My shouldered sleeve does not require ordering as soft collet,just use a nubbin.Turned and bored in one setup,it will run true.You can put the reamer between centers ,case rim closest to the tailstock,and use an indicator to follow the flute taper to set the compound angle. It will make 50 easily,and I would daresay TIR on all the rims/bodies will stay less than .001.We cant necessarily say reaming a soft collet would hold better concentricity. boring the soft collet with the taper attachment would be a better long term ,higher volume tool,but for 50 pcs,a sleeve with the compound in delrin will work.
just my opinion

Maybe I'm confusing a collet with a sleeve. Basically, I was talking about a device that would slide into a straight walled brass casing then it would expand just with enough force to grab the inside of the brass casing without stretching it. Help me out guys....I'm no machinist. Do I want to grab the outside of the brass or the inside...or does it matter if it is straight walled?

If you can figure out an arbor in your chuck that will get some friction on the ID of the case,yet still allow you to get the case back off,you have it made.
the id of a case has some taper,you can use that to advantage.
Suppose you clamp down your drill press vise in a way that lets you hold a lathe tool bit. if you bring your quill down slow past this cutter,you have rigged your spindle as a lathe,of sorts.If you use this to size your arbor,the arbor will run true. If you make your arbor stepped,2 diameters,it won't need to be tapered. maybe it will only fit tight for 3/16 or so. maybe you can use your calipers or an indicator to control how much you move the cutter. once you get it close,oversize,you can file a little to get your fit.
now that you have made your arbor,leave it in place,and you know how to turn your rim with the same cutter setup,bringing the quil down past the cutter. Now,it would probably be best to have a little negative rake on the top of your high speed cuter,so it scrapes rather than digging in.Brass likes that better,or it sucks in and will pull your piece off your mandrel. the cutter needs a sharp edge,hard india stone sharp. drag a thumbnail across it,it should cut a fine shaving. use cut and try to set your cut..004 a side is light,run a reasonable fast speed,maybe 500 to 1000 rpm,feed slow and careful. you can use your spindle stop nut to help,touch it,spin the nut 20 or 30 degrees,comedown and touch the nut,and so on.
good luck. oh,you might slip just the right open end wrench over the case body to tap the rim,to get the case off the arbor.
This may not work out with a $59 Harbor Freight drill press,the spindle can't flap around.A short spindle,don't hang it way out,will help,Some faily heavy oil in the workings of the spindle travel may help.Oil film strenghth can center things and damp a bit.Sometimes a little drag on the quill lock will take up some slop.

To answer your collet question: Your drill press cant use them.Its a lathe thing,but,yes,there are expanding 5c collets that could work,but no,it would not make sense,as a standard straight 5c collet in a lathe would hold them fine(I asked about your parent case a while back,all this was assuming atapered case.There is probably a way to get a precision hole,drill bushing or a reamed hole that is just a slip fit,spin the case inside the hole .clamp a lathe bit down so it turns the rim as you turn the case inside the hole.
Once again,if I may ask,why not alter the gun a bit to make this unnecessary?

The revolver is 45 Colt. It requires a rim of 0.512 max. 45 Colt Schofield has a rim of 0.520. They are straight walled cases. I don't want to modify the revolver as it should be easier to just reduce the rim of the 45 Schofield brass rather than send the cylinder off to a gunsmith.

I have a drill press and 50 pieces of 45 Schofield brass. If anyone has a good idea of what I need to purchase to reduce the rim by 0.008 please let me know. I don't think I want to buy a lathe.

.008 isnt much. Seems to me if you have a dial indicator, you could chuck the brass in the drill press. Have a grind stone on the DP table. Start the Drill press and bring the brass onto the stone, applying pressure until the dial indicator tells you you've move the brass down .008.

Maybe I'm making too big a deal about it. Guess I just didn't want to have to crank down the chuck on my brass to hold it. Afraid it might damage it. Thought there was a more delicate way to hold it....like with an expanding collet that could be chucked in the drill press.

Jmorris,I understand that.30 years of prototyping,modelmaking,moldmaking.I have machined plenty of soft collets and soft jaws. great tools.
Suppose you have a 4 flute reamer in a 3 slit collet.3 flutes are under cutter pressure while 1 flute is jumping the gap in the slit in the collet. that cutting edge is jumping an interrupted cut while the cutter pressure fom the other 3 flutes wants to deflect it into the cut. murphy's law tells me when the full length of that straight flute cutting edge jumps the collet slot the reamer will spring over a bit(remember,the reamer pilot is not running on a rifle bore) and a dig in MAY happen on that flute.

I have only used 6 flute reamers in collets before and had no problems. I would imagine a piloted reamer like the 30-06 one below would work fine too.

If you wanted to be safe and ensure that an intermittent cut had no chance of messing you up that too is an easy solution. Just insert shims into the relief cuts so they fill the gap while you machine the collet. This same method is used when you machine split set collars as well.

Quote:

Basically, I was talking about a device that would slide into a straight walled brass casing then it would expand just with enough force to grab the inside of the brass casing without stretching it.

In that case (no pun intended) why not just chuck the case up in the chuck and cutter in the vise? It works...

If you had to hold the case by some other method. For straight walled, you could also machine an expanding arbor like these but it would be a pain as you would have to put the expander in from the rear as you couldn’t get a large enough Allen wrench through the flash hole.

One other option is that you could make a wedge lock like below, this would be the least concentric but I bet you could get it to work too.

Sounds like that is my solution then...just chuck them up in the drill press.

Does anyone have any good ideas on what to use to cut the brass? Do I just hold a stone to the brass and guess, then stop, measure, then do it again? Maybe there is a better way that is both inexpensive and precise. Perhaps a Harbor Freight solution?

I used an end mill a minute ago because that is what I have close to the mills and drill presses. If I were going to setup to do a bunch of them from time to time I would use a HSS tool bit like this. They only cost a few bucks and would last a life time for what you want them for. They would also clamp in a vise better.

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